Compressor and hermetic housing with minimal housing ports

ABSTRACT

A vapor compression system having a multi-stage compressor with a minimal number of ports located in the hermetically sealed compressor housing. A working fluid at suction pressure enters the compressor housing through a first port and is compressed to an intermediate pressure. The intermediate pressure refrigerant flows from the first stage compressor mechanism to the second stage compressor mechanism where it is compressed to a discharge pressure and discharged through a second port. The intermediate pressure refrigerant is in thermal communication with a heat exchange medium which is introduced into the compressor housing through a third port in the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hermetically sealed compressor for avapor compression system and, more particularly, to a compressor housinghaving a minimal number of housing ports.

2. Description of the Related Art

A vapor compression system typically includes at least a compressor, afirst heat exchanger, an expansion device, and a second heat exchangerfluidly linked in serial order. Other components such as accumulators,flash tanks, and the like are also well-known and may be employed withthe vapor compression system, but are not essential for the operation ofthe vapor compression system.

One known type of vapor compression system is a transcritical vaporcompression system wherein the refrigerant is compressed to asupercritical pressure and is returned to the compressor at asubcritical pressure. When the refrigerant is at a supercriticalpressure, the liquid and vapor phases of the refrigerant areindistinguishable and the first heat exchanger is typically referred toas a gas cooler instead of a condenser. After cooling the refrigerant inthe gas cooler, the pressure of the refrigerant is reduced to asubcritical pressure by the expansion device and the low pressure liquidis communicated to the evaporator where the refrigerant is converted toa vapor.

When carbon dioxide is used as a refrigerant, the vapor compressionsystem is typically operated as a transcritical system and generallyrequires the use of a discharge pressure that is considerably higherthan the discharge pressure used with conventional refrigerants in asubcritical system.

To provide the relatively high discharge pressures required in atranscritical system, the compressor in a transcritical vaporcompression system is often a multi-stage compressor. The use ofmulti-stage compressors, such as a two-stage compressor, is known andsuch compressors typically include first and second stage compressormechanisms mounted at opposite ends of a drive motor. The drive motor isdrivingly linked to each of the first and second stage compressormechanisms by a common drive shaft. In general, the drive shaft iscoupled to the first and second stage compressor mechanisms in a mannerthat the first and second stage compressor mechanisms are out of phasewith respect to one another and/or at different points in thecompression cycle. To provide a relatively high pressure differentialbetween the suction and discharge pressures, the compressor mechanismsmay be arranged in series. Multi-stage compressor assemblies also ofteninclude an intercooler wherein intermediate pressure refrigerant iscooled by ambient air in a heat exchanger after being compressed by afirst compressor mechanism before being returned to the compressorassembly for compression to the discharge pressure in a secondcompressor mechanism.

FIG. 1 provides a schematic illustration of a known vapor compressionsystem 10 that includes gas cooler 12, expansion device 14, evaporator16, and two-stage compressor 18 connected in series by a plurality ofconduits 19. Compressor 18 includes first stage compressor mechanism 20and second stage compressor mechanism 22 arranged in series and mountedin the compressor housing schematically represented by dashed line 24.During operation of the two-stage compressor 18, suction pressurerefrigerant enters housing 24 through first port 26 and flows into firststage compressor mechanism 20 where it is compressed to an intermediatepressure. The intermediate pressure refrigerant then exits compressor 18through second port 28 and enters intercooler 30 where it is cooled. Bycooling the intermediate pressure refrigerant, the efficiency andcapacity of second stage compressor mechanism 22 are typicallyincreased. The cooled intermediate pressure refrigerant is then returnedto the compressor assembly through third port 32 into second stagecompressor mechanism 22. The intermediate pressure refrigerant is thencompressed to discharge pressure and discharged from compressor 18through fourth port 34.

A problem with the foregoing compressor mechanism is that the compressorhousing requires as many as four or more ports, each of which include anopening in the compressor housing which requires a seal, therebyincreasing the cost of the compressor and the number of locations on thecompressor housing at which a fluid leak could potentially occur.

What is needed is a compressor and for transcritical vapor compressionsystems which is an improvement over the foregoing.

SUMMARY OF THE INVENTION

The present invention provides a multi-stage compressor having a reducednumber of ports located in the compressor housing. The intermediatepressure refrigerant is cooled between the first and second compressorstages by a flash gas which is introduced into the compressor housingthrough a single port in the housing. Alternatively, a heat pipe orother heat transfer device may be inserted through a single port in thehousing of the compressor assembly to provide a thermal exchange withthe intermediate pressure refrigerant.

The invention comprises, in one form thereof, a compressor assemblyoperable in a vapor compression system defining a fluid circuit forcirculating a vapor. The compressor assembly includes a hermeticallysealed housing with a first and second compressor mechanism beingdisposed in the housing. The first and second compressor mechanisms areoperable to compress the vapor in two stages, wherein the firstcompressor mechanism compresses the vapor from a suction pressure to anintermediate pressure and the second compressor mechanism compresses thevapor from the intermediate pressure to a discharge pressure. Thehousing defines first, second, and third ports. The first and secondports are in fluid communication with the fluid circuit wherein suctionpressure vapor is communicated from the fluid circuit to the compressorassembly through the first port and discharge pressure vapor iscommunicated from the compressor assembly to the fluid circuit throughthe second port. The third port defines a passage for a heat exchangemedium wherein thermal energy is transferable between the heat exchangemedium and the compressor assembly. Further, all vapor circulatingwithin the circuit and all heat exchange mediums communicated throughthe housing are communicated through one of the first, second, and thirdports.

The invention comprises, in another form thereof, a transcritical vaporcompression system having a compressor assembly, a first heat exchanger,an expansion device and a second heat exchanger serially disposed in afluid circuit circulating a refrigerant. The compressor assemblyincludes a hermetically sealed housing with a first and secondcompressor mechanism being disposed in the housing. The first and secondcompressor mechanisms are operable to compress the refrigerant in twostages, wherein the first compressor mechanism compresses therefrigerant from a suction pressure to an intermediate pressure and thesecond compressor mechanism compresses the refrigerant from theintermediate pressure to a discharge pressure. The housing definesfirst, second, and third ports. The first and second ports are in fluidcommunication with the fluid circuit wherein suction pressurerefrigerant is communicated from the fluid circuit to the compressorassembly through the first port and discharge pressure refrigerant iscommunicated from the compressor assembly to the fluid circuit throughthe second port. The third port defines a passage for a heat exchangemedium wherein thermal energy is transferable between the heat exchangemedium and the compressor assembly. Further, all refrigerant circulatingwithin the circuit and all heat exchange mediums communicated throughthe housing are communicated through one of the first, second, and thirdports.

The invention comprises, in a further form thereof, a method ofcompressing a refrigerant. The method includes hermetically sealing afirst compressor mechanism and a second compressor mechanism in ahousing. The method also includes forming first, second, and third portsin the housing and introducing the refrigerant into the housing throughthe first port. The method further includes compressing the refrigerantin the first compressor mechanism from a suction pressure to anintermediate pressure; and compressing the refrigerant in the secondcompressor mechanism from the intermediate pressure to a dischargepressure. The method includes discharging the refrigerant from thehousing through the second port. The method also includes communicatinga thermal exchange medium through the third port; exchanging thermalenergy between the intermediate pressure refrigerant and the thermalexchange medium; and wherein all refrigerant and thermal exchange mediumcommunicated through the housing is communicated through one of thefirst, second, and third ports.

An advantage of the present invention is that same provides amulti-stage compressor mechanism wherein intermediate pressurerefrigerant may be cooled without requiring an intercooler and the twohousing ports associated with the use of an intercooler. The eliminationof the intercooler is beneficial because it may simplify the manufactureof the compressor assembly.

The reduction in the number of ports required in the hermetically sealedhousing is also beneficial because each of the ports of the housing mustbe properly sealed to ensure that the housing provides a hermeticallysealed enclosure and an increase in the number of ports in the housingincreases the chances that one of such ports may later develop a leakand may also increase the initial cost of manufacturing the compressorassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a schematic view of a prior art vapor compression system;

FIG. 2 is a schematic view of a first embodiment of a vapor compressionsystem having a compressor in accordance with the present invention;

FIG. 3 is a schematic view of a second embodiment of a vapor compressionsystem having a compressor in accordance with the present invention; and

FIG. 4 is a schematic view of a third embodiment of a vapor compressionsystem having a compressor in accordance with the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplifications set outherein illustrate embodiments of the invention, the embodimentsdisclosed below are not intended to be exhaustive or to be construed aslimiting the scope of the invention to the precise forms disclosed.

DETAILED DESCRIPTION

Referring to FIG. 2, vapor compression system 40 is a closed loop fluidcircuit through which a working fluid is circulated. Vapor compressionsystem 40 has operably disposed therein, in serial order, first heatexchanger 42, expansion device 44, second heat exchanger 46, andcompressor assembly 48. In the illustrated vapor compression system 40,the working fluid is carbon dioxide and vapor compression system 40 is atranscritical system. Consequently, first heat exchanger 42 is a gascooler wherein the carbon dioxide within gas cooler 42 is at asupercritical pressure while the carbon dioxide within second heatexchanger or evaporator 46 is at a subcritical pressure. The componentsof vapor compression system 40 are fluidly connected by a plurality ofconduits 49. Although a charge of carbon dioxide flows through the fluidcircuit in the illustrated embodiments, other refrigerants mayalternatively be employed with the present invention.

The use of carbon dioxide as the refrigerant requires vapor compressionsystem 40 to operate as a transcritical vapor compression system,wherein the high pressure side of the system is at a pressuresubstantially greater than a vapor compression system using aconventional refrigerant in a subcritical system. During operation ofvapor compression system 40, carbon dioxide is conveyed to compressorassembly 48 from evaporator 46 at a relatively low suction pressure. Thecompression of the carbon dioxide increases its temperature and pressureto a higher discharge temperature and pressure which, in the illustratedsystems employing carbon dioxide as the refrigerant, will be asupercritical pressure. The discharged refrigerant is then conveyed togas cooler 42 where the refrigerant is cooled. The high pressurerefrigerant exhausted from gas cooler 42 is then delivered to expansiondevice 44 where the pressure of the refrigerant is reduced. Therelatively low pressure refrigerant is then conveyed to evaporator 46.When employing carbon dioxide as the refrigerant, the carbon dioxidewill be reduced to a subcritical pressure by the expansion device 44.The relatively low pressure refrigerant will enter evaporator 46including liquid phase refrigerant wherein thermal energy is transferredto the low pressure refrigerant and liquid phase refrigerant withinevaporator 46 is converted to a vapor or gaseous state. The low pressurerefrigerant vapor is then returned to compressor assembly 48 and thecycle is repeated.

Such a vapor compression system may be used in various applications thatare well known in the art. For example, gas cooler 42 can be used toprovide heat for heating air in a heat pump application, or heatingwater in a water heater application. In other applications, evaporator46 may be used for cooling purposes such as in an air conditioning orrefrigeration applications.

Compressor assembly 48 in vapor compression system 40 is a hermeticallysealed multi-stage compressor having at least two compressor mechanisms.The compressor assembly may include any suitable type of compressormechanism including rotary, scroll and reciprocating piston compressors.Compressor assembly 48 is schematically illustrated in FIG. 2 having ahermetically sealed housing represented by line 50. Compressor assembly48 is a two-stage compressor including first stage compressor mechanism52 and second stage compressor mechanism 54. Housing 50 defines interiorplenum 51 in which first and second stage compressor mechanisms 52 and54 are located. Compressor mechanisms 52 and 54 may be mounted onopposite ends of a common drive shaft driven by an electric motor (notshown) located within housing 50. The compressor mechanisms 52 and 54are advantageously mounted out of phase from one another or at differentpoints in the compression cycle to provide a more balanced load on themotor.

Compressor assembly 48 may be a low side compressor in which interiorplenum 51 is filled with suction pressure refrigerant. The suctionpressure refrigerant is at a lower temperature than the compressedrefrigerant and facilitates the cooling of the motor. The presentinvention is not limited to low side compressors, however, andalternative embodiments may employ a variety of configurations includinghigh side compressor designs wherein the motor cavity is filled withdischarge pressure refrigerant.

During operation of compressor assembly 48, suction pressure refrigerantis compressed in first stage compressor mechanism 52 to an intermediatepressure. The intermediate pressure refrigerant passes through conduit56 located within housing 50 and fluidly linking first stage compressormechanism 52 and second stage compressor mechanism 54. The intermediatepressure refrigerant is cooled while in conduit 56 by means which willbe described further hereinbelow. The cooled, intermediate pressurerefrigerant is then compressed in second stage compressor mechanism 54to a higher, discharge pressure.

Cooling the intermediate pressure refrigerant in a two-stage compressorassembly between first stage compressor mechanism 52 and second stagecompressor mechanism 54 improves the efficiency and capacity of thesecond stage compressor mechanism and thus compressor assembly 48. Inthe present invention, the lack of an intercooler 30 (FIG. 1) externalof the compressor mechanism 52 eliminates the need for one of the portsin compressor housing 50 while still providing means for cooling theintermediate pressure refrigerant. The elimination of one port incompressor housing 50 is advantageous in that the number of connectionsbetween compressor assembly 48 and the fluid circuit of vaporcompression system 40 are reduced. Further, by using alternative means,described below, to cool the intermediate pressure refrigerant whilesame passes between first stage compressor mechanism 52 and second stagecompressor mechanism 54, an intercooler 30 (FIG. 1) is not necessary,thereby reducing the number of components of vapor compression system40.

Compressor housing 50 is provided with three ports 58, 60, and 62. Firstand second ports 58 and 60 provide passages through which refrigerantgas is communicated to and from compressor assembly 48 to the vaporcompression circuit. The suction pressure refrigerant enters compressorhousing 50 through first port 58 formed in the housing and is directedinto first stage compressor mechanism 52. The discharge pressure gascompressed by second stage compressor mechanism 54 is discharged fromcompressor housing 50 through port 60. Third port 62 defines a passagethrough which a heat exchange medium enters compressor housing 50 tocool the intermediate pressure gas passing from first stage compressormechanism 52 to second stage compressor mechanism 54.

Referring to FIG. 2, a means of transferring thermal energy between aheat exchange medium and compressor assembly 48 is illustrated. Asdiscussed above, discharge pressure refrigerant is exhausted fromcompressor assembly 48 and is conveyed to gas cooler 42. In gas cooler42, heat is transferred from the high pressure refrigerant to ambientair or other heat exchange medium. The temperature of high pressurerefrigerant in gas cooler 42 is thereby reduced. The refrigerant thenpasses through expansion device 44 where the pressure of the refrigerantis reduced resulting in a mixture of vapor and liquid phase refrigerant.

In the embodiment of FIG. 1, a portion of the low pressure, vapor phaserefrigerant exiting the expansion device 44 is diverted as a flash gasto compressor assembly 48 where it provides a heat exchange medium forcooling the compressor assembly including intermediate pressurerefrigerant. Conduit 64 defines a fluid passage for the flash gas havinga first end of conduit 64 fluidly linked to the vapor compression systemfluid circuit at a location between expansion device 44 and evaporator46. The second end of conduit 64 is in fluid communication with interiorplenum 51 of compressor housing 50 via third port 62. A valve 66 may beoperably positioned along conduit 64 to control the flow of flash gasthrough conduit 64.

In alternative embodiments, conduit 64 may divert refrigerant fromanother location in vapor compression system 40 to compressor assembly48. For example, the flash gas may be diverted from a locationdownstream of evaporator 46. Conduit 64 may also include an expansiondevice to further reduce the pressure, and consequently the temperature,of the flash gas which is conveyed to the compressor assembly 48. Theuse of an expansion device also allows refrigerant to be diverted from alocation upstream of expansion device 44 to provide the flash gasentering compressor assembly 48 through third port 62.

The relatively low pressure and temperature flash gas is conveyed byconduit 64 provides a heat exchange medium for cooling the intermediatepressure refrigerant in conduit 56. The flash gas enters compressorassembly 48 through third port 62 and fills interior plenum 51 ofcompressor housing 50, surrounding conduit 56. As the intermediatepressure refrigerant flows through conduit 56, heat is transferred fromthe intermediate pressure refrigerant to the flash gas in interiorplenum 51, thus reducing the temperature of the intermediate pressurerefrigerant prior to entering second stage compressor mechanism 54. Inthis embodiment, compressor assembly 48 is a low side compressor withlow pressure gas filling interior plenum 51.

Referring to the embodiment illustrated in FIG. 3, the vapor compressionsystem includes compressor assembly 70 having a hermetically sealedhousing 74 and a thermal exchange device 72.

As with the previous embodiment shown in FIG. 2 and described above,first stage compressor mechanism 52 and second stage compressormechanism 54 are positioned within interior plenum 76 of housing 74 andare fluidly linked by conduit 78. Suction pressure refrigerant enterscompressor housing 74 through first port 80 and is compressed to anintermediate pressure in first stage compressor mechanism 52. Theintermediate pressure refrigerant flows through conduit 78 into secondstage compressor mechanism 54 where it is compressed to a dischargepressure and discharged to gas cooler 42 through second port 82. Heatingor cooling device 72 is mounted in third port 84 formed compressorhousing 74 so as to exchange thermal energy between the interior andexterior of housing 74. For example, device 72 may be a heat pipe thatcools the interior of the compressor assembly 48, including theintermediate pressure refrigerant in conduit 78.

Conduit 78 is provided with a second passage 86 extending substantially,for example, perpendicularly to conduit 78. Passage 86 is closed at theinternal end and the opposite end sealingly engages the internal surfaceof compressor housing 74 in surrounding relationship of third port 84such that the intermediate pressure refrigerant in conduit 78 does notleak into interior plenum 76. Sleeve 88 is sealingly mounted in thirdport 84 and extends into passage 86 with a portion of sleeve 88 being incommunication with conduit 78. Heating or cooling device 72 ispositioned within sleeve 88. As intermediate pressure refrigerant flowsalong conduit 78 from first stage compressor mechanism 52 toward secondstage compressor mechanism 54, a thermal exchange occurs between heatingand cooling device 72 and the intermediate pressure refrigerant tomodify the temperature of the refrigerant and thus control theefficiency of compressor assembly 70. Device 72 may be in the form of aheat pipe, for example, or the like.

The heat transfer device 72 may be a heat pipe, thermosyphon or othersuitable device. Heat pipes and thermosyphons are commonly used toprovide a heat transfer device within laptop computers, for example, andare well known to those of ordinary skill in the art. Heat pipes andtubular thermosyphons may take the form of an elongate tube having asealed interior volume. A fluid is provided within the sealed interiorvolume and provides a heat transfer medium. One end of the devicefunctions as an evaporator and at this end of the device liquid phaseworking fluid is evaporated thereby providing a cooling effect. Thevaporized working fluid migrates to the opposite end of the device whereit is condensed and returns to a liquid phase thereby exhausting thermalenergy to the surrounding environment. The condensed liquid phaseworking fluid returns to the evaporator end of the device either bymeans of gravity or through a wicking effect provided by a porous medialocated within the interior volume.

FIG. 4 illustrates a third embodiment of the present invention. In thisembodiment, compressor assembly 90 includes a heating or cooling device92 extending through compressor housing 94 and which transfers thermalenergy between the interior and exterior of housing 94. Suction pressurerefrigerant enters compressor housing 94 through first port 96 and iscompressed to an intermediate pressure in first stage compressormechanism 52. The intermediate pressure flows through conduit 95 intosecond stage compressor mechanism 54 where it is compressed to adischarge pressure and discharged through second port 98. Heating orcooling device 92 is mounted in third port 100 formed in compressorhousing 94 and is in thermal communication with the intermediatepressure refrigerant in conduit 95.

Conduit 95 is provided with a second passage 102 extending substantiallyperpendicularly to, for example, conduit 95. Passage 102 is closed atthe internal end and the opposite end sealingly engages the internalsurface of compressor housing 94 in surrounding relationship to thirdport 100 such that the intermediate pressure refrigerant in conduit 95does not leak into interior plenum 104 defined by housing 94. Openings106 extend in a direction substantially parallel, for example, toconduit 95 and are formed near the internal end of passage 102. Openings106 are in fluid communication with oil located in interior plenum 104.

A first sleeve 108 is mounted in passage 102 in thermal communicationwith openings 106. A second sleeve 110 is positioned adjacent firstsleeve 108 with one end sealingly mounted in third port 100 such that aportion of second sleeve 110 is in communication with conduit 95. Wall112 is located in passage 102 to prevent fluid communication between theoil passing through openings 106 and intermediate pressure refrigerantflowing through conduit 95. Sleeves 108 and 110 are concentricallypositioned to receive heating or cooling device 92. Device 72 may be inthe form of a heat pipe, for example, or the like.

As intermediate pressure refrigerant flows along conduit 95 from firststage compressor mechanism 52 toward second stage compressor mechanism54, a thermal exchange occurs between heating and cooling device 92 andthe intermediate pressure refrigerant to alter the temperature of therefrigerant. In addition, oil flows through openings 106 and aroundsleeve 108 so that a thermal exchange may occur between the oil andheating and cooling device 92 to control the temperature thereof andthus the efficiency of compressor assembly 90.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

1. A compressor assembly operable in a vapor compression system defininga fluid circuit for circulating a vapor, said compressor assemblycomprising: a hermetically sealed housing; a first compressor mechanismdisposed within said housing; a second compressor mechanism disposedwithin said housing, wherein said first and second compressor mechanismsare operable to compress the vapor in two stages wherein said firstcompressor mechanism compresses the vapor from a suction pressure to anintermediate pressure and said second compressor mechanism compressesthe vapor from the intermediate pressure to a discharge pressure; andwherein said housing defines first, second and third ports, said firstand second ports in fluid communication with said fluid circuit whereinsuction pressure vapor is communicated from the fluid circuit to saidcompressor assembly through said first port and discharge pressure vaporis communicated from said compressor assembly to the fluid circuitthrough said second port, said third port defining a passage for a heatexchange medium, wherein thermal energy is transferable between the heatexchange medium and said compressor assembly, and wherein allsuperheated or wet vapors circulating within the circuit and all heatexchange mediums communicated through said housing are communicatedthrough one of said first, second and third ports.
 2. The compressorassembly of claim 1 wherein the heat exchange medium is a flash gas andsaid third port is in communication with an interior plenum defined bysaid housing, said first and second compressor mechanisms disposedwithin said interior plenum.
 3. The compressor assembly of claim 1wherein said interior plenum of said housing is at suction pressure. 4.The compressor assembly of claim 1 wherein said compressor assemblydefines a flow path between said first compressor mechanism and saidsecond compressor mechanism for intermediate pressure vapor and the heatexchange medium transfers thermal energy with the intermediate pressurevapor.
 5. The compressor assembly of claim 4 wherein the heat exchangemedium is a flash gas and said third port is in communication with aninterior plenum defined by said housing, said first and secondcompressor mechanisms disposed within said interior plenum.
 6. Thecompressor assembly of claim 1 further comprising a heat transfer deviceextending through said third port.
 7. The compressor assembly of claim 6wherein said heat transfer device is a heat pipe.
 8. The compressorassembly of claim 1 wherein said third port is in communication with asleeve, said housing defining an interior plenum, said sleeve extendingwithin said plenum and defining an elongate volume in communication withsaid third port and sealingly separated from said plenum.
 9. Thecompressor assembly of claim 8 further comprising a heat transfer deviceextending through said third port and partially disposed within saidsleeve.
 10. A transcritical vapor compression system comprising: acompressor assembly, a first heat exchanger, an expansion device and asecond heat exchanger serially disposed in a fluid circuit circulating arefrigerant; said compressor assembly comprising: a hermetically sealedhousing; a first compressor mechanism disposed within said housing; asecond compressor mechanism disposed within said housing, wherein saidfirst and second compressor mechanisms are operable to compress therefrigerant in two stages wherein said first compressor mechanismcompresses the refrigerant from a suction pressure to an intermediatepressure and said second compressor mechanism compresses the refrigerantfrom the intermediate pressure to a discharge pressure; and wherein saidhousing defines first, second and third ports, said first and secondports in fluid communication with said fluid circuit wherein suctionpressure refrigerant is communicated from the fluid circuit to saidcompressor assembly through said first port and discharge pressurerefrigerant is communicated from said compressor assembly to the fluidcircuit through said second port, said third port defining a passage fora heat exchange medium, wherein thermal energy is transferable betweenthe heat exchange medium and said compressor assembly, and wherein allrefrigerant circulating within said vapor compression system and allheat exchange mediums communicated through said housing are communicatedthrough one of said first, second and third ports.
 11. The compressorassembly of claim 10 wherein the heat exchange medium is a flash gas andsaid third port is in communication with an interior plenum defined bysaid housing, said first and second compressor mechanisms disposedwithin said interior plenum, the flash gas comprising relatively lowpressure refrigerant diverted from said fluid circuit from a locationbetween said expansion device and said compressor assembly.
 12. Thecompressor assembly of claim 10 wherein said compressor assembly definesa flow path between said first compressor mechanism and said secondcompressor mechanism for intermediate pressure refrigerant and the heatexchange medium transfers thermal energy with the intermediate pressurerefrigerant.
 13. The compressor assembly of claim 12 wherein the heatexchange medium is a flash gas and said third port is in communicationwith an interior plenum defined by said housing, said first and secondcompressor mechanisms disposed within said interior plenum, the flashgas comprising relatively low pressure refrigerant diverted from saidfluid circuit from a location between said expansion device and saidcompressor assembly.
 14. The compressor assembly of claim 10 furthercomprising a heat transfer device extending through said third port. 15.The compressor assembly of claim 10 wherein the refrigerant comprisescarbon dioxide.
 16. A method of compressing a refrigerant, said methodcomprising: hermetically sealing a first compressor mechanism and asecond compressor mechanism in a housing; forming first, second andthird ports in said housing; introducing the refrigerant into saidhousing through said first port; compressing the refrigerant in thefirst compressor mechanism from a suction pressure to an intermediatepressure; compressing the refrigerant in the second compressor mechanismfrom the intermediate pressure to a discharge pressure; discharging therefrigerant from the housing through said second port; communicating athermal exchange medium through said third port; exchanging thermalenergy between the intermediate pressure refrigerant and the thermalexchange medium; and wherein all refrigerant and thermal exchange mediumcommunicating through said housing is communicated through one of saidfirst, second and third ports.
 17. The method of claim 16 wherein saidstep of communicating a heat exchange medium through said third portcomprises introducing a flash gas into said housing through said thirdport.
 18. The method of claim 17 wherein said refrigerant comprisescarbon dioxide and the discharge pressure exceeds the critical pressureof the refrigerant.
 19. The method of claim 16 wherein communicating aheat exchange medium through said third port comprises extending a heatpipe through said third pipe.